Advances in polymerization and catalysis have resulted in the capability to produce many new polymers having improved physical and chemical properties useful in a wide variety of superior products and applications. With the development of new catalysts, the choice of polymerization-type (solution, slurry, high pressure or gas phase) for producing a particular polymer has been greatly expanded. Also, advances in polymerization technology have provided more efficient, highly productive and economically enhanced processes. Regardless of these technological advances in the polyolefin industry, common problems, as well as new challenges still exist. For example, the tendency for a gas phase process to foul and/or sheet remains a challenge, which can particularly be dependent on the polymer being produced and the catalyst system employed.
Fouling, sheeting and/or static generation in a continuous gas phase process, in for example heat exchangers, distributor plates, and probes, can lead to the ineffective operation of various reactor systems. In a typical continuous gas phase process, a recycle system is employed for many reasons including the removal of heat generated in the process by the polymerization reaction.
Evidence of, and solutions to, various process operability problems, including fouling, sheeting, chunking, and agglomerating and static build up, have been addressed by many in the art. For example, U.S. Pat. Nos. 4,792,592, 4,803,251, 4,855,370 and 5,391,657 all discuss techniques for reducing static generation in a polymerization process by introducing to the process for example, water, alcohols, ketones, and/or inorganic chemical additives; PCT publication WO 97/14721 published Apr. 24, 1997 discusses the suppression of fines that can cause sheeting by adding an inert hydrocarbon to the reactor; U.S. Pat. No. 5,066,736 and EP-A1 0 549 252 discuss the introduction of an activity retarder to the reactor to reduce agglomerates; EP-A1 0 453 116 discusses the introduction of antistatic agents to the reactor for reducing the amount of sheets and agglomerates; U.S. Pat. No. 4,012,574 discusses the addition of a surface-active compound, a perfluorocarbon group, to the reactor to reduce fouling; U.S. Pat. No. 5,026,795 discusses the addition of an antistatic agent with a liquid carrier to the polymerization zone in the reactor; U.S. Pat. No. 5,410,002 discusses using a conventional Ziegler-Natta titanium/magnesium supported catalyst system where a selection of antistatic agents are added directly to the reactor to reduce fouling; U.S. Pat. No. 3,470,143 describes a reduction in fouling in mostly slurry processes for producing primarily elastomers using a fluorinated organic carbon compound.
Likewise, further evidence of, and solutions to, various process operability problems have been addressed by many in the art. For example, U.S. Pat. No. 3,082,198 discusses introducing an amount of a carboxylic acid dependent on the quantity of water in a process for polymerizing ethylene using a titanium/aluminum organometallic catalysts in a hydrocarbon liquid medium; U.S. Pat. No. 3,919,185 describes a slurry process using a nonpolar hydrocarbon diluent with a conventional Ziegler-Natta-type or Phillips-type catalyst and a polyvalent metal salt of an organic acid having a molecular weight of at least 300; U.S. Pat. No. 5,990,251 relates to increasing catalyst activity of a Ziegler-Natta-type catalyst by using very small quantities of a halogenated hydrocarbon, specifically a molar ratio between 0.001 and 0.15 of the halogenated hydrocarbon, particularly chloroform, to the metal of the catalyst, specifically titanium; U.S. Pat. No. 6,455,638 is directed to a polymer blend having components with different ethylene content, and U.S. Pat. No. 5,624,878 relates primarily to the use in polymerization of catalytic derivatives of titanium (II) and zirconium (II) metallocene-type complexes; both U.S. Pat. Nos. 6,455,638 and 5,624,878 mention generally, in passing, using in polymerization various solvents such as straight-chain hydrocarbons, cyclic and alicyclic hydrocarbons, perfluorinated hydrocarbons, aromatic and alkyl-substituted aromatic compounds, and mixtures thereof. U.S. Pat. No. 6,534,613 describes using a Ziegler-Natta-type catalyst in combination with a halogenated hydrocarbon, particularly chloroform, and an electron donor to produce polymers useful for making better quality films. EP 1 323 746 shows loading of biscyclopentadienyl catalyst onto a silica support in perfluorooctane and thereafter the prepolymerization of ethylene at room temperature. U.S. Pat. No. 3,056,771 discloses polymerization of ethylene using TiCl4/(Et)3Al in a mixture of heptane and perfluoromethylcyclohexane, presumably at room temperature.
It has been unexpectedly found that, the practice of this invention allows higher concentrations of induced condensing agents and thus allows higher production rates without fouling.
Thus, it would be advantageous to have a gas phase polymerization process capable of operating continuously with enhanced reactor operability, or a polymerization process having the ability to produce an expanded range of product capabilities on a commercial scale.